1. Field of the Invention
The present invention relates to a node device arranged at every transmission section for cross-connection in a transmission system adapted to a synchronized transmission mode and a maintenance and operation supporting device linked with the node device for maintaining a link and a path based on the cross-connection.
2. Description of the Related Art
With a novel synchronous digital hierarchy (SDH), it is possible to achieve synchronization of various signals including a low rate group and a high rate group, flexible edition of transmission information for the high rate group as well as supervisory, inspection and control in connection with various maintenance and operation in the transmission path, so that the SDH has been widely used in not only a trunk line system such as B-ISDN but also a private network.
FIG. 9 is a diagram showing a network configuration applied to the novel synchronous digital hierarchy.
In FIG. 9, a plurality of node devices 42-a to 42-d are arranged in a network 41 formed in a ring type as a unidirectional path switched ring (UPSR) and duplexed based on an active redundancy, and these node devices 42a to 42d are connected to a supervisory and control device 51 via a LAN 52.
Among these node devices 42-a to 42-d, the node devices 42a include the following elements:                a plurality of high-speed interface (HIF) units 43W-a and 43E-a respectively connected to two transmission sections immediately next to the network 41;        a cross-connector (XC) unit 44-a arranged between the afore-mentioned high-speed interface units 43W-a and 43E-a;        a path switch (PSW) 45-a cascade-connected to two low-speed outputs of the cross-connector unit 44-a corresponding to the afore-mentioned high-speed interface units 43W-a and 43E-a, respectively;        a low-speed interface unit (LIF) 46-a interfacing between an output of the path switch 45-a and a low-speed input of the cross-connector unit 44-a to each of communication devices (not shown) accommodated into the node device 42-a;         a storage memory (HM) 47-a connected to a control termination of one side of the cross-connector unit 44-a; and        a supervisory and control unit 48-a connected to a control termination of the other side of the cross-connector unit 44-a and the control termination of the path switch 45-a, or connected to the LAN 52.        
The node devices 42-b to 42-d have the basically same construction as that of the node device 42-a, so that identical reference numbers with additional characters ‘b’ to ‘d’ instead of ‘a’ refer to like parts which have the similar function and structure. The detailed description thereof will be omitted herein.
In the network constructed as described above, the respective node devices 42-a to 42-d linked as mentioned below are cross-connected in predetermined rate group units (e.g., a path having a transmission rate of 52 Mbps) so that a predetermined path is provided in the communication device accommodated into the node devices 42-a to 42-d through the network 41.
Hereinafter, an additional character ‘C’ which represent any one of the additional characters ‘a’ to ‘d’ refers to the common characteristics that can be applied into any of the node devices 42-a to 42-d. 
In addition, hereinafter, for any of the transmission section provided between the node devices 42-a to 42-d, additional characters indicating two nodes arranged at both sides of the corresponding transmission section will be individually attached (e.g., additional character ‘ab’ refers to a transmission section from the node device 42-a to the node device 42-b).
The storage memory 47-C stores control information on paths provided between the preceding and following transmission sections of the network 41 and between the communication device accommodated into the node device 42-C and either one of the transmission sections, as station information (including station information updated by the supervisory and control unit 48-C).
The cross-connector unit 44-C provides all paths indicating station information between the preceding and following transmission sections of the network 41, and between the communication device accommodated into the node device 42-C and either one of the transmission sections.
In addition, the path switch 45-C selects a low-speed output corresponding to the path to be individually connected to the communication device (corresponding to one of the input side between the two adjacent transmission sections) among the low-speed outputs of the cross connector unit 44-C, under the control of the supervisory and control unit 48, and connects the selected low-speed output to the low-speed interface unit 46-C.
In addition, while in maintenance and operation, for example, when the transmission sections ab is to be released due to extension of node installation or inspection subject, each unit is connected as described below.                The supervisory and control device 51 totally manages an active path provided through any one of the transmission sections ab, bc, cd, da, ad, dc, cb, and ba and an auxiliary path prepared in advance within a redundant transmission capacity of the respective transmission sections to be used in place of the active path.        When an operator assigns the transmission section ab as a transmission section to be released, the supervisory and control device 51 specifies all of the paths (hereinafter, referred to as a specific path, individually) provided via the transmission section ab.        Under the afore-mentioned control, the supervisory and control device 51 specifies an auxiliary path that can individually substitute the specific path, and informs the operator of an identifier of the corresponding specific path and identifiers of node devices arranged at both ends of the specific path, for either of the auxiliary path, based on a predetermined man machine interface.        Furthermore, when either end of the specific path is assigned by the operator, the supervisory and control device 51 updates system configuration information in connection with the corresponding specific path (and provided to the afore-mentioned control) and transmits a ‘switching instruction’ comprising identifiers of the specific path and auxiliary path to the two node device destinations arranged at both ends of the corresponding auxiliary paths through the LAN 52.        The supervisory and control unit 48-C that can be individually arranged in the afore-mentioned two node devices of the node devices 42-a to 42-d instructs the path switch unit 45-C to replace the specific path indicated by the identifiers included in the ‘switching instruction’ by the auxiliary path.        
However, in the example of the prior art, the ‘switching instruction’ is not transmitted to any of the node device destinations as long as the operator does not assign the specific path, and transmitted to two node device destinations arranged at both ends of the specific path for every specific path assigned by the operator.
Therefore, when the transmission section ab is released due to the extension of the node installation or the inspection subject, manual tasks should be performed many times (the maximum counts will be ‘192’ that is equal to the number of rate groups to be cross-connected at every bit rate of 52 Mbit/sec in case of the rate group having a bit rate of 10 Gbyte/sec), and thus, to exactly assign every path without missing, a man machine interface should be provided with which ‘proper information concerning the actual system configuration’ can be precisely provided to the operator and fault operation is accurately prevented.
However, in the rate group of the transmission section to be cross-connected, in particular, in the network of the trunk line system, there is a high probability that increasing demand on transmission service of the data system may lead to shifting of much higher rate group, so that there is a strong demand for technology in which the man hour that takes to release the desired transmission section can be increased and degradation of certainty regarding the releasing can be significantly reduced.